Evaluation of the Effectiveness of Natural Ventilation in Greenhouse, SUDAN

الملخص

Natural ventilation is an effective and economical strategy for maintaining a suitable greenhouse microclimate during hot periods, particularly when average daily temperatures range between 12 °C and 22 °C. This study evaluated the effectiveness of natural ventilation in multi-tunnel greenhouses, specifically analyzing the effects of vent area, wind speed, and insect-screen porosity on air exchange rates and thermal performance. A theoretical modeling approach based on greenhouse energy balance equations was employed to calculate ventilation rates and inside–outside temperature differences across various vent configurations. Climate data (wind speed, temperature, and solar radiation) were obtained from long-term historical records to ensure representative modeling conditions. The presence and size of ventilation openings on both the roof and sidewalls strongly influence air exchange rates and the resulting inside–outside temperature difference. The results demonstrated that insect-proof screens significantly reduced ventilation capacity, with low-porosity meshes causing the greatest significant reduction in airflow, and these reductions cannot be fully compensated unless vent openings are enlarged. Increasing the vent-to-floor area ratio from approximately 25–25.5% to about 40% restored adequate ventilation performance in screened greenhouses, enabling air exchange coefficients above 29 h⁻¹ and maintaining temperature differences within the desirable range of 1–2 °C. Under conditions of high solar radiation, the combined effects of ventilation and shading further improved greenhouse thermal performance. However, during periods of prolonged high outdoor temperatures, natural ventilation alone becomes insufficient, indicating the need for complementary cooling strategies. Overall, this study highlighted the critical role of vent dimensions and insect screen porosity in greenhouse ventilation design and provided practical guidance for optimizing natural ventilation in semi-arid climates.